You will have to cut open those bottles and scrape out any softish gel with toothpicks.

You can add vodka, glycerine, any clear extract or piping gel to soften. You will have to grind the lumps with something like a mortar and pestle or you will have lumps in your icing. No mortar, then use the back of a teaspoon on a small plate. Lots of mess to clean up but you should be able to rescue enough to do this cake.